1) Field of the Invention
The present invention relates to a method and apparatus for removal of material from a body of material and, in particular but not exclusively, to a method and apparatus for removal of material to form a bore during drilling operations.
2) Description of Related Art
Currently known methods of plasma or electric arc drilling rely on the process of heating the material to be removed to its melting point. This process requires a significant amount of electrical power, and has the further difficulty of accurately focussing the power source on the material, or formation, which is to be removed. This may, therefore, result in the production of wide “kerfs” being formed during the process of producing a bore, as well as the waste of electrical power.
Another known method is spark drilling which utilises an electro-hydraulic shockwave, initiated by a plasma discharge, which propagates through a fluid medium and impinges on the material causing the material to disintegrate or fracture. The major difficulty with this process is focussing the shockwave onto the material. If the shockwave is not focussed much of the shockwave energy is wasted resulting in a poor “drilling” rate. In addition, the resulting hole is not a clearly defined, circular borehole.
It is an object of the present invention to obviate or mitigate at least one of the problems associated with the prior art.